stragali Radix (Huangqi) is an important Chinese herbal medicine that is always processed into pieces for clinical use. There are many operations required after harvesting, among which drying of AR pieces is a key step. Unfortunately, research on the drying mechanism is still limited.
Low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) techniques were applied to study the water status and water distribution during the drying process. The contents of bioactive ingredients and texture changes were measured by HPLC and texture analyzer, respectively.
During the drying process, the moisture content first decreased rapidly. After a particular time, the moisture content decreased slowly, and the equilibrium value was reached. The trends for changes in flavonoid glycoside and flavonoid aglycone contents in AR pieces were entirely opposite. The relaxation times T22 and T23 and the peak areas A22 and ATotal decreased significantly during drying. In addition, the intensity of the water signal decreased from the surface to the interior. The textural parameters hardness, adhesion and fracturability increased without an apparent change in springiness. The parameters of LF-NMR and the texture analyzer were correlated with water content.
This study indicated that HPLC, LF-NMR, MRI and texture analyzers provide a scientific basis for elucidating the principles for drying of AR pieces. The method is useful and shows potential for popularization and application; accordingly, it can easily be extended to other radix and/or rhizoma Traditional Chinese Medicinal materials.